The invention relates to a silver halide photographic light-sensitive material (hereinafter referred to as a light-sensitive material), and more particularly to a light-sensitive material that is highly sensitive and relatively less in fog and is further remarkably reduced in the dependence of gradations on illuminance.
In recent years, there have been increased demands for highly sensitive light-sensitive materials from various points of view, and the sensitizing techniques have been studied from various aspects.
As an example of the studies concerning a silver halide particle, there is the description of the study in which the quantum efficiency of a silver halide particle is theoretically computed and the influence of the particle size distribution is examined, in `Interactions Between Light and Materials for Photographic Applications`, the preprint of Tokyo Symposium, 1980, p. 91. According to this study, it is suggested that the preparation of a monodisperse emulsion is effective to improve a quantum efficiency, that is to say, it is possible to highly sensitize the emulsion.
In order to actually obtain a highly sensitive emulsion, it is still necessary to chemically sensitize the silver halide emulsion most suitably, even if such a highly sensitizable silver halide emulsion as described above is used. As the sensitizing agents to be used in a chemical sensitization, a sulfur sensitizer, a selenium sensitizer, a reduction sensitizer, a noble metal sensitizer and the like have so far been well-known, and they may be used independently or in combination. In addition, there have been the studies of how to further improve the sensitization effects by making use of such a chemical sensitizer as mentioned above. For example, as has been disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter called Japanese Patent O.P.I. Publication) No. 30747/1983, there has been disclosed a method that a chemical sensitization is carried out in presence of a silver halide solvent. A particularly useful method is that, as described in Japanese Patent O.P.I. Publication No. 126526/1983, a chemical sensitization is to be carried out in presence of a nitrogen-containing heterocyclic compound capable of forming a complex with silver. After having continued a further study, the present inventors have found that, when a sulfur sensitization is carried out in presence of a nitrogen-containing heterocyclic compound capable of forming a complex with silver, a high sensitization can be achieved in particular with keeping down the fogs substantially. The findings mean that the method of sulfur sensitization carried out in presence of a nitrogen-containing heterocyclic compound capable of forming a complex with silver is remarkably effective to make a light-sensitive material highly sensitive without increasing fogs. However, it was also found that this remarkably effective sensitizing method still has a serious problem, that is, the gradations will greatly be varied according to the illuminance of an exposure light. It has so far been a well-known phenomenon that a sensitivity will be varied by changing a illuminance even if an exposure light quantity remains as it is the same. To this phenomenon, the countermeasures have been taken to change an exposure light quantity so as to correspond to a predicted sensitivity change or in like manner, therefore, the phenomenon does not affect so much in practical use.
Nevertheless, if a gradation change cause by an exposure light illuminance (hereinafter called a gradation dependence on illuminance) is great, the light-sensitive material will be vitally affected in quality. Light-sensitive materials are so designed in accordance with the purposes of their usage as to desirably differentiate the gradations each. When actually exposing such a light-sensitive material to light, the exposure illuminance thereto is naturally changed in accordance with the exposure conditions, for example, the brightness of a photographic object and the like in the case of a photographing light-sensitive material, and an image-density difference caused by the over- or under-exposure of an original photo-film in the case of a light-sensitive material for prints. In a light-sensitive material having a great gradation dependence on illuminance, the actual gradations thereof are shifted out of the permitted limit of the gradations of the target provided in the designing stage.
Therefore, the reproductions of images vary, according to the scenes photographed, sometimes to become so hard that the low- and high-density areas in particular can not be described, or sometimes to become so soft that the images will come out dull without any brilliance. In any case, the qualifications for the light-sensitive materials will be seriously damaged in quality.
In the light-sensitive materials for printing use, there are available a variety of print sizes which are popularly ranged from so-called E-size that is a small size up to the size of 18'.times.22'. Ordinarily, there are many cases where most of the users will try first to make a print in small size from the scenes photographed, and select therefrom some preferred scenes so as to make the enlargement into a larger size. In this instance, the original film is the same in either cases of printing one scene into a small size or a large size, and the intensity of a light source is also difficult to greatly increase. Therefore, when enlarging an image to a large-sized print, it cannot be avoided that an exposure illuminance to a light-sensitive material for printing use is lowered. As the result thereof, in the case that a gradation dependence on illuminance is great, an image-quality will be deteriorated in a large-sized print even if a desired image-quality may be obtained in a small-sized print, therefore, the users are unsatisfied.
The variations of a sensitivity caused by an exposure illuminance have not become a serious problem in practical use because an exposure means has been improved, however, the variations of gradation are very difficult to avoid by improving such an equipment as an exposure means or the like. It is, therefore, desired to improve a gradation dependency on illuminance, from the viewpoint of light-sensitive materials.